Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells per device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to one another because high output and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is possible to easily modify the shape of the pouch-shaped battery.
In order for the middle or large-sized battery module to provide output and capacity required by a, specific apparatus or device, it is necessary for the middle or large-sized battery module to be configured to have a structure in which a plurality of battery cells is electrically connected in series to each other or in series and parallel to each other and the battery cells are stable against external force.
In addition, the battery cells constituting the middle or large-sized battery module may be secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from such high-output, large-capacity secondary batteries during charge and discharge of the secondary batteries. If the heat, generated from the unit battery during charge and discharge of the unit battery, is not effectively removed from the unit battery, the heat accumulates in the unit battery with the result that deterioration of the unit battery is accelerated. According to circumstances, the unit battery may catch fire or explode. For this reason, a bat pack for vehicles, which is a high-output, large-capacity battery, needs a cooling system to cool battery cells mounted ire the battery pack.
Meanwhile, a power storage device is generally configured to have a structure in which a plurality of battery packs is mounted in a rack in a drawer type packaging manner. Drawer type packaging means inserting a series of battery packs in one rack in a state in which the battery packs are vertically stacked. In a case in which a cooling system is configured for the battery packs provided in the power storage device, it is difficult to achieve high cooling efficiency in a structure in which battery modules are arranged in a state in which a flow channel is vertically formed in each battery module to cool battery cells or unit modules.
That is, it is difficult to provide a space necessary to form the flow channel at the upper part and the lower part of each battery pack because the battery packs are vertically stacked. For this reason, it is necessary to dispose the battery modules in a state in which the battery modules are laid down such that the battery packs are mounted in a drawer type packaging manner in order to achieve cooling while improving spatial efficiency.
In addition, the power storage device requires high energy density and uniform lifespan and performance of the batteries. Consequently, a compact design is needed even when the rack is configured as well as when the battery pack is configured.
For spatial utilization, for example, battery modules may be disposed in a battery pack 100 and coolant flow channels may be formed in the battery pack 100 as shown in FIG. 1. In a case in which the battery modules are arranged in a direction in which the coolant flow channels are formed, however, external air is directly introduced into first row battery modules but air having absorbed heat from the first row battery modules, i.e. heated air, is introduced into second row battery modules. As a result, cooling efficiency of the second row battery modules is lower than that of the first row battery modules, whereby lifespan of battery cells constituting the battery modules is shortened.
In order to solve the above problem, a battery pack 100a having separate coolant inlet ports formed therein as shown in FIG. 2 has been proposed. In a case in which the coolant inlet ports are separated from each other as described above and a coolant flow gap is provided in the battery pack, however, coolant introduced through one of the coolant inlet ports adjacent to a coolant outlet port is dispersed and cools battery modules away from the coolant outlet port. As a result, flow distributions of the coolant at the respective battery modules are different from each other, which may cause asymmetric temperature patterns in the respective battery nodules and local cooling deviation.
Consequently, there is a high necessity for technology to fundamentally solve the above problems.